The present invention relates to a charged particle beam lithography apparatus for forming a pattern on a semi-conductor memory by utilizing a charged particle beam, and relates to a projection mask used for said charged particle beam lithography apparatus.
A conventional charged particle beam lithography apparatus, especially an electron beam lithography apparatus is used for research and development as an exposure apparatus for exposing a minute pattern referring to its high resolution. In the mass-production of the devices however, throughput of the charged particle beam lithography apparatus is low compared with that of an optical exposure apparatus, and the cost performance thereof is inferior.
Late years, a cell projection exposure method by which patterns are repeatedly loaded on a stencil mask beforehand, and the exposure is performed in a high reduction rate by deflecting optically so as to select the pattern, attracts attention. For example, such method is indicated in Japanese Patent Laid-open No. 6-163377. As in this cell projection exposure method, the complicated shape patterns are exposed together, a shot number is reduced largely, and high throughput may be obtained.
Furthermore, this cell projection exposure method is possible to expose in high accuracy too, because there is not a measurement setting error (by location gap of mask) as in a variable shaped beam type exposure beam formation method (Japanese Patent Laid-open No. 4-100208), in which the pattern that should be exposed is formed by overlapping two or more masks.
However, the cell projection exposure method has a problem as that only several ten patterns having exposure area of practically used several um are obtained to be selected. In order to increase the pattern number, a complicated pattern selecting deflection system which is capable to be deflected with a great angle becomes to be needed, furthermore, there is a problem in accuracy such as distortion of a stencil pattern and deterioration of matching accuracy and switching accuracy between mutual figures, because of aberration by an optical separating axis, deflection response, and increase of drift.
Moreover on a mask board top, in order to form a pattern which exceeds a selection range of the optical system, a drive mechanism as indicated in Japanese Patent Laid-open No. 7-183191 may be arranged, it takes an enough time for selecting the pattern by driving the mechanism, and there arises a problem in order to obtain the high throughput.
An object of the present invention is to solve the problems stated above and is to provide a charged particle beam lithography apparatus which remarkably increases the pattern number which can be selected by a cell projection exposure method and is capable to realize the high throughput.
In order to solve the problems stated above, a charged particle beam lithography apparatus in the present invention comprises a charged particle source to generate a charged particle beam, and a plurality of stencil masks which respectively have several transferal apertures generating patterns which should be projected on a specimen by a charged particle beam from the charged particle source. Thereby, in the case when projection is performed by a transferal aperture of at least one of the stencil mask among said several stencil masks, the charged particle beam is irradiated on the specimen passing through outside of the transferal aperture of other stencil masks among the several stencil masks.
According to the constitution of the charged particle beam lithography apparatus stated above, it becomes possible to provide a plurality of stencil masks respectively having plural transferal apertures. Moreover there is no affection by the measurement setting error of the stencil mask arranged in several steps too, and a lot of transferal apertures becomes possible to be provided in high accuracy.
Moreover, as a constitution to realize a more concrete embodiment of the present invention, a transfer mechanism to transfer the stencil mask and a control part which controls a charged particle beam deflector arranged in a circumference of an optical path of the transfer mechanism and the charged particle beam, are provided.
Furthermore, according to the present invention, a control part for controlling the transfer mechanism is provided, and said control part moves an exposure location of the charged particle beam toward the transferal aperture of the other stencil masks when the charged particle beam is irradiated relating to the transferal apertures of one or more stencil mask.
Even if the stencil masks are provided in several steps, a continuous writing using the plural transferal apertures may be realized in high throughput.
Moreover, because this transfer is performed by the transfer mechanism while the charged particle beam is positioned outside of a transmission aperture or the stencil mask, other stencil masks may be projected before the next writing during the pictures are written by at least one of the stencil mask.
As a transmission aperture is formed along the sequence of the transferal aperture formed on the stencil mask furthermore, the exposure location of the charged particle beam moves to the neighborhood of the transferal aperture which should be projected (or moves until said transferal aperture enters in a deflection range of the charged particle beam) before the stencil mask moves, thereby, it becomes possible to position the exposure location of the charged particle beam in the transferal aperture immediately when the projection is performed by using the transferal aperture.
Moreover, the plural stencil masks may be provided at an equal height to an optical axis of charged particle beam. In this case, when patterns are written by the transferal aperture of one of the stencil masks, the transfer mechanism is controlled so as to position the transferal aperture of the other stencil masks in the deflection range of the deflector of the charged particle beam, Thereby, after the writing by the transferal aperture of one of the stencil mask is finished, the writing by next transferal aperture becomes possible to be done immediately, and many transferal apertures may be provided while maintaining high throughput.
As stated above, the stencil masks arranged in several steps (or plural stencil masks in the same height) are provided, are positioned by the transfer mechanism, and expose the transferal apertures on the stencil masks successively.
Moreover in order to realize the high throughput, when selectively exposing the specified stencil mask aperture group by the cell projection deflector, the charged particle beam transmits the non-screening parts of the other stencil mask (the transmission aperture). Here, the stencil mask non-screening parts are provided in succession towards a mask transfer direction, the other stencil mask are executed to be transferred when exposing the specified stencil mask aperture group while letting the beam transmit. The above stated operations are repeated, thereby the exposure is controlled to complete. According to the above stated constitution of the present invention, it becomes possible to reduce the transit time by the transfer mechanism which takes much time comparing with the exposure location transfer of the charged particle beam by the charged particle deflector, and to expose continually by the cell projection exposure method.
The number of the apertures which are capable to be used in the present invention is limited by the product of the transferal aperture number of the stencil masks and the stencil mask number. For example, usual reduction rate is about one per several ten, and size of the stencil mask aperture to realize a cell projection exposure method of several um is 100 um around. Accordingly when the transferal aperture is loaded by an occupation rate of 10%, it becomes possible to select 1000 apertures with the stencil mask of 10 mm square. If plural stencil masks are arranged, it becomes possible to mount several thousand exposure apertures by the cell projection method.